Enzymatic measures reflecting oxidative stress (NA-AAF-UDS and ADPRT) have been associated with colorectal neoplasia (odds ratios 7+ population attributable risks 40-61%), and a similar assay (UVC-UDS) was associated with breast cancer (odds ratio-7+, PAR%-45%). The primary aim of this study is to examine the hypothesized association between breast cancer and inter-related enzymatic measures of oxidative stress, NA-AAF-UDS, UVC-UDS, ADPRT, and GT-teBSO, in a case-control study of 440 women 9160 breast cancers, 160 benign breast disease controls without atypia, 120 non-neoplasia controls). All participants provide an interview for risk factors and venous blood for assays. Overall statistical power is 85-99% (2-sided p<0.05) to detect odds ratios of 2.5 to 3.0. Sex hormones might distort the relationship of these markers to breast cancer, and the UVC- UDS marker may help avoid this problem via its non-chemical induction of UDS by UV light. Also, as a secondary aim, studies of several sex hormones are planned. Funding of biochemical expenses is supported by PMI-Strang Clinic, complemented by The Small Grant Award, which would be used here for epidemiology. The study meets the Award's criteria of ".. developing a test for future epidemiologic research..". Such development is needed to plan definitive longitudinal studies of cancer, particularly of the colorectum and breast, using these promising enzymatic markers. Abbreviations: UVC-UDS: Unscheduled DNA synthesis induced by ultraviolet light of C band; NA-AAF -UDS: unscheduled DNA synthesis induced by N- Acetoxy-N-2 fluroenylacetamide; ADPRT: adenosine diphosphate ribosyl transferase: GT-tsBO: Glutathione Transferase isoenzyme trans-stilbene oxide.